This invention relates to a rotary anode X-ray tube provided with a pair of bearings rotatably supporting a rotary anode portion.
Generally, in rotary anode X-ray tubes of this type, the rotary anode portion is rotated at such a high speed as e.g. 9,000 rpm in a high-vacuum atmosphere. As for the bearings rotatably supporting the rotary anode portion, they are heated to such a high temperature as approximately 450.degree. C. because heat produced by the rotary anode emitting X-rays is transmitted thereto through a rotating shaft. Therefore, the bearings will more severely be worn away, damaged, or displaced as compared with other members, and it is generally said that the life of the rotary anode X-ray tube depends upon the life performance of the bearings.
Accordingly, in one such prior art rotary anode X-ray tube, the bearings are incorporated therein by fixing with high accuracy their inner and outer races to the outer peripheral surface of the rotating shaft of the rotary anode portion and the inner peripheral surface of an anode support, respectively. Since the bearings are used under circumstances of high vacuum and high temperature, as aforesaid, they cannot be of the commonly used oil-lubricating type. Therefore, the bearings used are of a solid-lubricating type in which the inner and outer races and rolling bodies are plated or coated by chemical vapor deposition with gold, silver, lead or other material. As compared with oil-lubricating bearings, however, the solid-lubricating bearings are subject to increased play or reciprocal eccentricity depending upon the manner of assembly and/or use, in spite of high-accuracy assembly. Accordingly, there will be caused substantial vibration and noise in and around the bearings, and such vibration and noise will be increased quickly, thus deteriorating the life performance of the bearings and hence of the rotary anode X-ray tube.